Since you only mention cruise lines with no additional info on interests, ports, etc, my answer is pretty easy. If you are just going to decide on Celebrity vs RCI (we like both lines) I would suggest RCI because of their superior programs for the kids. However, you also should consider that most European cruises are different than what you have experienced in the Caribbean. Med cruises are often quite port intensive and there is often not a lot of time spent on the ships. Ports are quite varied in Europe so I have a suggestion. Take a close look at the ports of the various cruises, and ask your kids for their input on which ports capture their interest and what they really would like to do with their port days. As an example, some kids really want to see Pompeii (port of Naples) while others might want to see Paris (port of LeHavre). Letting the kids help with the decision, and having them spend some time researching the ports and tour options, can be fun and its also very educational.